1. Field
One or more embodiments relate to a multibeam light source unit, a method of adjusting the unit, a light scanning unit, and an electrophotography type image forming apparatus, and more particularly, to a multibeam light source unit in which adjustment of light sources is easy in an assembly process, a method of adjusting the unit, a light scanning unit, and an electrophotography type image forming apparatus.
2. Description of the Related Art
An electrophotography type image forming apparatus, such as a laser printer, a digital copying machine, and a multifunction printer (MFP), has a structure in which by emitting a light beam to a photoreceptor through a light scanning device, an electrostatic latent image is formed, the formed electrostatic latent image is developed to a development image by using a developer such as a toner, and the development image is transferred on a printing medium.
In an image forming apparatus, a multibeam light scanning unit, which records a plurality of lines by using a plurality of light beams, may be used in order to improve the printing speed. A multibeam light scanning unit uses a light source, which emits at least two light beams (hereinafter, referred to as a multibeam), such as a multibeam laser diode. For the image forming apparatus to implement a color image, the light scanning unit has a plurality of light sources to be modulated by an image signal corresponding to image information of a plurality of single colors, for example, black (K), magenta (M), yellow (Y), cyan (C).
In a multibeam light scanning unit, adjustment of interval between beams of a multibeam may be performed by rotating light sources. For example, as illustrated in FIG. 1, a multibeam light scanning unit includes a light source 1 fixed to an optical housing 8 by using a light source holder 5. The light source holder 5 may be coupled with the optical housing 8 by using screws. Adjustment of intervals between beams of the light source 1 may be performed by pressing the light source 1 into the light source holder 5 and grabbing and turning a grip unit 5A of the light source holder 5. As an example, as illustrated in FIG. 2, an optical scanning unit has a structure in which an LD unit 40 is formed by pressing two laser diodes 54 and 55 into a holder 55 with a leaf spring 65 pressing the LD unit 40 into an installation hole of an optical housing 60. Adjustment of rotation of the LD unit 40 is performed by turning an adjustment screw 71 of an adjustment device maintenance unit 58.
In the rotation adjustment structure of the conventional multibeam light scanning unit, there are problems of deformation in a fixing process after adjusting a light source, and vulnerability to external environment changes. For example, in a structure in which a light source holder is fixed to an optical housing by a coupling unit, such as screws, even though a grip unit of the light source holder is fixed, the optical housing and the light source holder may be deformed by variation in the coupling power of the screws, the order of coupling the screws, and changes in the coupling torque. In a structure in which a light source holder is equipped with an elastic unit, such as a leaf spring, variation in the spring tension occurs because of the simple fixing by the spring tension, and a gap as big as the allowance between the optical housing and the light source holder occurs. This structure is vulnerable to external shock. Also, when the internal and external temperatures of the multibeam light scanning unit increases, it is highly likely that a deformation occurs because of the asymmetrical shape of the light source holder. Because of these problems, the position of a beam emitted from a light source changes and the position on the surface of a photoreceptor becomes incorrect.
When an existing single light beam is used, the sensitivity of the rotational angle of a light source may not matter. However, when a multibeam, formed with two or more light beams is used, the sensitivity of the rotational angle of a light source increases. For example, in order to maintain an existing performance, the angle tolerance of a light source using two beams may be, for example, approximately 14 degrees. However, when a light source using four beams is used, the angle tolerance may be, for example, within 1.5 degrees and thus the sensitivity increases, for example, by 9.3 times or more. In an image forming apparatus using one beam, deterioration in the picture quality due to this problem may be small, but in a color image forming apparatus using a plurality of light sources with a plurality of photoreceptors, this causes incorrect image colors and thus degrades the quality of an image.
A light scanning unit using a tilted incident beam may reduce the size and material cost of a light scanning unit having a plurality of mounted light sources because it has compact light path layout and smaller number of parts. In a light scanning unit using a tilted incident beam, a plurality of light sources may be disposed with narrow intervals. However, it is not easy to mount a plurality of light sources with narrow intervals because of issues of size, shape, and fixing method of light source holders that are used in the conventional assembly of light sources.